Process for oxidation of aromatic hydrocarbons



NOV. 29, v1949 w, F, RQLLMAN 2,489,347

PROCESS FOR OXIDATION OF AROMATIC HYDBOCARBONS W. F. ROLLMAN PROCESS FOROXIDATION OF ARDMATIC HYDROGARBONS Filed Aug. l1, 1945 Nov. 29, 1949 3Sheets-Sheet 2 Pull.

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STEAM Ouw- Guber-neg Patented Nov. 2 9, 1949 UNITED STATES PATENT OFFICEPROCESS FOR OXIDATION F AROMATIC HYDBGCARBON S Walter F. Bollman,Cranford, N. J., assigner to Standard 0il Development Company, acorporation of Delaware Application August 1l, 1945, Serial No. 610,346

l 2 Claims. (Cl. 26o-342) This invention relates to an improved methodthe depth of the catalyst mass and, more particufor the oxidation ofaromatic hydrocarbons and larly, by using a coarse catalyst. pertainsmore particularly to the manufacture of The invention will be moreclearly understood phthalic anhydride, from the following detaileddescription read in The oxidation of aromatic hydrocarbons, suchconjunction with the accompanying drawings as naphthalene andorthoxylenc, to phthalic anwhich form a part of this specificationwherein hydride and maleic anhydride is a well-known Figure 1illustrates in schematic form one method process. In the usual process amixture of the for carrying out the invention, Figure 2 is a dearomatichydrocarbon and air is passed through tailed view of the reactor ofFigure 1 shown in a bed of an oxide catalyst, such as vanadium m sectionand Figure 3 illustrates a modiiled form oxide at a temperature between570 and 1200 of reactor. F. Because of the exothermic nature of the re-As charging stocks for Vthe process of this inaction it has beendiilicult to properly control the vention, there may be used anysuitable aromatic temperature of the reaction zone and prevent thehydrocarbon or aromatic hydrocarbon stock such formation of hot spotsand local overheating. :5 as coal tar distillates, refractory stocksproduced It has recently been proposed to overcome these by catalyticcracking orreforming, or pure arodimculties by eii'ecting the oxidationby means of matic hydrocarbons such as orthoxylene, napha iinely dividedsolid or powdered catalyst mainthalene, alkyl naphthalenes, etc. tainedas a turbulent dense phase mass in the -As catalysts for this processthere may be emreaction zone. u ployed 6th or 7th group metal oxideseither sup- It has been considered necessary that the cataported orunsupported on suitable carriers such lyst should be very fine, that isabout 200 to 400 as alumina, silica gel, pumice. kieselguhr. corunmesh,and should be used in relatively thick beds l dum, or any other knowncatalyst supports. It

several feet high. However, such ilne catalyst is is a particularfeature of this invention to employ Y diillcult to maintain in the fluidstate because of .5 unsupported catalyst in the form of spheres havitstendency to go overhead with the eilluent ing a particle size between 10and 60 mesh, prefergases and to cling to the upper part of the reactorably between and 40 mesh. Such spheres may when the feed is introduced.Furthermore, the be prepared in any well known manner. A suituse of suchthick beds increases materially the able method consists in obtainingparticles of contact time of the hydrocarbon with theoxidizapproximately the desired size and then fusing ing mediumresulting in increased formation of them into spheres by dropping theparticles carbon dioxide and carbon monoxide due to a through a heatedquartz tube. This is accomcorresponding degradation of the desiredprodplished by initially fusing the oxide either alone ucts ofoxidation. or in admixture with any desired promoter, for

It is therefore the main object of this invenexample. potassium sulfate,in a muiile furnace tion to provide an improved process for the oxide'.-and pouring the resulting melt onto a quartz tion of aromatichydrocarbons using powdered surface where it is allowed to cool in thinsheets.

catalyst. The crystallized oxide is then ground and It is a furtherobject of this invention to descreened and particles of the desired sizeare crease the cost of manufacturing phthalic anhy- 40 fed slowlythrough a quartz tube heated to 1700"- dride and maleic anhydride and toincrease the 1800*' F. wherein the particles melt and assume yields ofthese compounds from aromatic hydroa. spherical shape. The meltedparticles are then carbons.- solidified by a free fall of several feetthrough Other objects of the invention will be apparent cool air. Thecooled spheres thus formed are as the detailed description proceeds.collected and screened to size.

In practicing this invention the oxidation of The process will now bedescribed in connection the aromatic hydrocarbons is edected by meanswith the use of a fused spherical vanadium oxide of a relatively coarsecatalyst in the form of catalyst of 20-40 mesh for the preparation ofspheres in a reaction zone under oxidizing conphthalic anhydride fromnaphthalene, although ditions, with air and hydrocarbon vapors flowingit is to be understood that the invention is not concurrently upwardthrough the masst of catalimited to any particular catalyst compositionor lyst contained in the reaction zone. The flow preparation, or to theoxidation of any particular of vapors and air is so controlled that thecatalyst feed stock or to the use of any particular type particles areconstantly in motion. of apparatus.

It is a feature of this invention to increase Referring, therefore, tothe drawings there is the yields of desired reaction products byaffordprovided a reactor I0 containing a plurality of ing only briefcontact of the reactant gases with parallel tubes Il, having a diameterof 1 to 6 the catalyst at uniform conditions of time and inches,preferably 2 inches, containing layers of temperature. This isaccomplished according to catalyst I2 placed on grids I3 and connectingthe present invention by materially decreasing with inlet headers Il andexit header I5. Tubes il are surrounded by a liquid heat exchange mediumsuch as boiling water, fused salts, mercury, dipiienyl, diphenyl oxideand the like introduced through line i6 and removed through line l1.Water is preferred as the heat exchange medium because of its cheapnessand abundance and heat recovery is relatively simple. Completeflexibility of throughput is achieved by segmenting inlet header [l sothat if desired only part of the tubes need be used.. The tubes areconveniently arranged in separate groups to facilitate access ofYcooling water to tubes farthest from the jacket wall, and clean outdoors (not shown) are provided in the top head to permit easy additionor withdrawal of catalyst. The reactor may be started up by preheatingthe catalyst with combuston gas from burners on each inlet line, and theinside walls of the inlet chamber are insulated to prevent overheatingof the metal parts during this preheat period.

Air is introduced into the system through line 23 ai; a. pressure ofabout 15 to 30 lbs/sq. in., and naphthalene vapors plus air areintroduced from vaporizer 24 through line 25 and mixed with the air inline 23 in amounts of about 0.5 to 2.0 mol per cent, preferably 0.8 molper cent naphthalene in air. The mixture of naphthalene and air isintroduced into header I l of reactor ill through line 2E and branchlines 2T. From header l 4 vapors and air enter the bottom of each tubeIl through grids I3. A pressure drop of several pounds per square inchis maintained across grids i3 in order to insure uniformity ofdistribution of vapors to the several tubes Il. Catalyst contained inthe lower portion of the tubes is more or less violently agitated by therising vapors, but because of its coarse size is not carried overhead.Heat of reaction is removed through the walls of the tubes with the netresult that vapors leave the top of the tubes at a temperature of about400 to 600 F. Vapors and gases leave the tubes through header l5 andline I8 and are passed to recovery tower i9 where they are scrubbed withwater introduced through line 20. A solution of phthalic and maleicanhydride is removed through line 2i and fixed gases are taken overheadthrough line 22. Relatively pure phthalic 4 anhydride may he separatedfrom other conversion products by conventional processes.

In Figure 3 is shown a modification of reactor l0 which increases therange of feasible operating conditions. Referring therefore, to thisdrawing, reactor lll is shown fitted with a tube sheet 3l at a levelcorresponding approximately to the quench section of the tubes. Sheet 3|is provided with one or more overflow lines 32 connecting the spaceabove with the space below. In this modification the heat exchangemedium, e, g. water, is introduced through line I6 above the sheet andremoved through line l1 below the sheet. The water admitted above thesheet cools the quench section of the tubes and the excess flows throughthe overiiow line. 32 into the lower section wherein the reaction zoneltemperature is controlled. Heat transfer from the reaction zone in thetubes may be varied over wide limits by raising or lowering the level ofwater in the jacket which in turn is determined by the raie of wateraddition in the quench zone. The reaction temperature in the tubesshould be maintained between 900 and 1100 F.; preferably about 1050 F.The vertical gas velocity in the reactor should be about 1 to 10 ft. persecond, preferably 2" ft. per second. At such velocities the catalyst,particles will be in motion but generally will not be entrained in thegases leaving the reactor so that substantially identical temperaturesprevail throughout the entire mass.

An important feature of the invention is the very short contact timewithin the reactor which may range from 0.1 to 1 second. Optimum yieldsof phthalic anhydride are obtained with a contact time of about 0.5second. A. very convenient method of achieving this short contact timeis by the use of relatively shallow dense phase catalyst masses. Thedepth of the catalyst mass in the tubes ranges from 3 to 36 inches andis preferably 14 inches.

The following data illustrate the unexpected advantages obtained in theoxidation of naphthalene to form phthalic anhydride by using shortcontact times. shallow dense phase catalyst mass, and catalyst in theform of spheres of 20-40 mesh fused vanadium oxide.

Fluid catalytic vapor phase oxidation of naphthalene Catalyst FusedVanadium Oxido Type Micmephmc. Supported on corundnm l Size mesh 24H0Q40 lili-l2) 0) Superilcial Vapor Velocity, stfmafpe m sfafri'fm 2 l D1D e V8 i. Naphthaleno Feed Conc., mol o o rcent in air I. 0. 0.8 0.750.8 0.5 0.8

0 in 0.18 az om n.2 0.1 au Contact time. sec 0 5 0. 5 0. 3 Avg. Depth oicatalyst mm, n. 3 o 5 u'. .s l' '.3 L. L m o e m0 percen 5 94 77.

Phlhllic Anhydride----- 84 87 85 651 70.*5 a Malek* Anhydride 9 9. 5 910. 5 9. 5 5 get CO-SO: ....t.. 1m m5 9.5 17. 5 2&5

011V. T0011 selectivity tgelhthalic An l 87 1m hydride, percent 84. 5 8785 77. 0 71. 5 Q

l Difficulties in o rating with this catalyst were encountered as ittends to iiuii up" and goiover ead at reaction conditions; furthermore,it platos out on cooling surfaces included in the reactor to remove theheat o! reaction from tho system. 5W 0-20 microns 60.5%; 2040 microns29.9%; w-w microns 14.0%: w+ miams amasar From 'the above data it isclearly evident that unexpectedly high yields, high conversions and highselectivities are obtained by using microspherical catalysts in therange of 20-40 mesh for the oxidation of naphthalene. Furthermore thedata conclusively show that the use of supported catalyst in the rangeof 100-200 mesh is not practical because of the low yields and becauseof the operating difficulties encountered and the use of supportednon-spherical catalyst gives even lower yields. Thus 85-87% selectivityto phthalic anhydride at complete conversion is shown with the 20-40mesh catalyst compared to 77% selectivity at 87% conversion with 40-60mesh catalyst and only 71.5% selectivity at 98.5% conversion for the100-200 mesh catalyst. While this invention is not intended to belimited by any theory as to why certain results are obtained, it isbelieved that the fact that conversion is incomplete with the finercatalyst in spite of the larger surface area, potentially available, canbe attributed to the bypassing of the vapors around the catalyst andconversely the lower selectivity may mean that some vapors aremomentarily trapped in the voids between the catalyst particles and arethus vrxcontacted. In other Words it appears that the surface of the20-40 mesh catalyst is more eiciently used and contact of vapors andcatalyst is more uniform than when ner catalyst is used.

While one specic process embodying the novel steps of the presentinvention, as well as one speciilc apparatus for carrying out the samehas been described in considerable detail, it is to be understood thatthisdescription is illustrative only, and for the purpose of making theinvention more clear, and it is not intended that the invention shall beconstrued as limited to details of the description except insofar assuch limitations have been included in the terms of the following claimsin which it is the intention to claim all novelty inherent in theprocess according to the present invention.

`vapors that leave and pass above said reaction zone, and withdrawingsaid gas and vapors that leave the reaction zone from the upper part ofthe vertical tube.

2. The method as described in claim 1, wherein the aromatic hydrocarbonis naphthalene, said mass of spherical particles have a thicknessbetween 3 and 36 inches with a diameter of 1 to 6 inches in saidreaction zone, the vertical velocity of the oxygen-containing gas andthe vapors of the aromatics hydrocarbon is between 1 and 10 feet persecond to maintain said vapors in contact with the vanadium oxide for aperiod between 115 and 1 second, and a temperature of 900 to 1100" F. ismaintaihed in said reaction zone.

WALTER F. ROLLMAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,978,506 Punnett Oct. 30, 19342,081,272 Foster May 25, 1937 2,215,095 Drossbach Sept. 17, 19402,366,372 Voorhees Jan. 2, 1945 FOREIGN PATENTS Number Country Date170,022 Great Britain Oct. 7, 1921

